Friday, May 15, 2015

A portable B3?


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This "Portable B3" -project is the main reason why I decided to launch this HammondFinn blog some time ago. Basicly it's quite traditional Hammond chop, a try to get full console organ to more transportable form, but it's also my personal study of Hammond philosophy.

Weight and bulky shape have been main problems over the time Hammond organs have been used in live performances. Size can be reduced by cutting lower part off, but as upper compartment still contains all the heavy parts, it's not a real solution for portability. When it comes to non-musical aspects, the outlook of real console organ, B3 or C3, is quite often pretty important. And not the outlook only, but the real feel of solid and sturdy instrument instead of plastic keyboard on wobbling lightweight stand.

So my approach to the problem was to split weight to separate modules and still keep the original look and feel as far as possible. For this reason I ended up to build completely new housing so that I got freedom to form parts just as I wanted.

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The instrument splits now to six parts; upper compartment with keyboards only, tone generator unit, preamp unit, lower compartment with pedalboard contacts, pedalboard and bench. Electrical units are linked together with industrial grade multipole connectors, so basically there are three connectors to get the organ ready to play or move.

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As the project was an unique prototype, most of plans were in my head and formed out during actual work, which every now and then made progress really slow. I decided to use birch plywood for most parts of the housing, as my main target was to build up robust instrument for gigging musician.

Dimensions of original Hammond parts determined all measurements, so I needed to make certain modifications to get all the components fit in; for instance, preamp power transformer is now mounted beside preamp and expression pedal capacitor housing is turned on its side, both to reduce height of preamp case.

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I also wanted to keep the preset panel because it is one of typical console Hammond features, but as it couldn't be left on it's original place and position, I had to rebuild panel frame upside down, rewire it and match it to fit in free space. Switch is for selecting ground lift.

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All wooden parts are stained as cherrywood with slight reddish tint and finished with 2-component satin lacquer. There were several challenges to arrange proper conditions for air spray painting in workshop at my photostudio, but after all I was quite satisfied to results.

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Expression pedal was one of the most challenging part to solve; originally it has simple mechanic linkage from pedal to preamp housing, but as all of my units were now detachable and sealed, it was difficult to easily arrange any mechanical connections between them. My first try was to move expression capacitor housing from top of preamp to underneath pedal assembly and connect them together with shielded cable to avoid hum and noise on this high impedance part of circuit. It worked, but volume response had a nasty delay, obviously caused by increased length of wiring.

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I finally built expression control with a servo motor; the controller located on preamp housing reads value from potentiometer which is linked with expression pedal and then servo mechanically moves original control shaft.

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Another challenge related to high impedance amplifier circuits was wiring from vibrato scanner to preamp terminal "D". Although shielded, it is extremely sensitive to any interference and easily causes noise and hum, especially if the length of wiring is increased. After trying different types of shieldings and grounding points with results of different type buzzing and humming, I finally took separate short coaxial line with BNC connectors from generator unit to preamp unit and got rid of any noises. Other tone generator wirings remained quite close to their original length, so I didn't find problems with them.

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During years I have made several leslie modifications for solid state speed switching relays, so it was natural add-on here too. This organ was meant to be used with leslie 122, therefore I modified connection so that instead of practically useless B+ feed on pin 5, it is now used to send low level control voltage to solid state relays in the leslie amp. By this means I got rid of switching delays of original phantom voltage mixed in audio signal and also getting full slow-off-fast control by simple voltage polarity switching.

Same modification is even more functional with unbalanced type leslies (147, 145, 251... etc) as they originally use mains AC voltage to control original relay. In these systems switching sparks often cause electrical noises, but what I personally feel the most uncomfortable image, is having a lethal voltage inside fragile bakelite leslie switch body just underneath my fingers. The very same switch is mainly used as electric guitar pickup selector, so it's really not a perfect item to make any high voltage connections.

Naturally, the switch unit is meant to be easily detachable with two thumbscrews and robust XLR-connector.

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As the organ was almost completely parted during the project, I also made normal service operations like busbar cleaning. I renewed electrolytic capacitors from organ and leslie amplifiers too, as they are aging components anyway. Original organ used in this project was Hammond A100 from early 70's, so it had newer red mylar filter caps in generator and after all those service procedures overall tone was really bright, punchy and powerful. Most probably it was what all Hammonds have been when they rolled out from factory line, but in this case it was a kind of problem, because the new owner wanted it sound like mid 50's mellow jazz organ...

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Solution for this was recalibration of tone generator output voltages. There are available lot of measurement data of organs from different era, so I first measured actual voltages to make a chart to compare with all previous data charts. It showed up that the bright high end curve was similar to other late model organs (upper image), so I dropped higher tones down and raised first two octaves a bit to get it closer to older models (lower image). Module design of my project was now working like a dream, as I just lifted generator unit on bench, unscrewed lids to expose pickups from both sides and then temporarily connected mains to start and run motors.

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So, what are my conclusions after all efforts? Using term "portable" is maybe too extravagant in case of any old tonewheel Hammond, as the heaviest unit of the organ is still pretty heavy, although it won't break up your back so easily. Actually, the total weight is now even higher than original B3 due to extra housings, but on the other hand it is possible to divide to lighter components which was my original idea. The best solution in any case is use some kind of wheel dollies whenever it is possible, so the final stage to my project was making roll-or-kari -type simple wheel dollies from lightweight aluminium profile.

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Without generator and preamp units the organ is now noticeable easier to lift and handle on dollies. And in my humble personal opinion, it's a real beauty compared to any Hammond chops I have seen so far.

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12 comments:

  1. Hieno! Hienompi kun mun -65 L100 joka on rakennettu flightcaseen. Vaan eihän mulle mahtuisi enää lisää rämpyttimiä.

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  2. Unbelievable... Thumbs up!!!

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  3. this is a real nice job you did , but I should never start it , I have built chops but in a practical way , modify E100 organs and cut them in half this is a cheap organ with all the guts for B3 sound and still all tubes , by using E100 I do not destroy a valuable B3 or A100.. What I noticed is that you usezd silvercontact connectors , watch out silver oxidizes , why not using gold connectors ?? anyway congratulations on this job . Benjamin Belgium

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  4. Great Job !, but how long to set up at the gig !?.

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  5. could one person carry each piece?

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  6. What a fantastic job! Would you mind selling some of the plans for the cabinet? Really interested in picking you brain a bit, as I'm approaching a project simularly. I'm at peterkohlmetzmoller@gmail.com - Best, pete

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